1. Field of the Invention
The invention relates to a spacer screw, by means of which a structural member, such as, for example, a beam or a wall part, can be fixed to a base member at a variable distance.
There are spacer screws which have a thread section on their front end capable of penetrating into the base member, an anchoring section present at the opposite rear end and consisting of a plurality of annular ribs widening toward the screw head, and a threadless shank section in between. Such screws are disclosed, for example, in U.S. Pat. No. 4,808,051 and have the disadvantage that they are only of limited use. Thus, in this special case, the force to be applied when screwing the thread section into the base member must be so great that at the same time the anchoring section is driven into the structural member, which not only may result in undesired cracking and splitting but also requires the use of structural members which have lower strength than the base member.
2. Description of the Prior Art
To overcome these disadvantages, further spacer screws have been disclosed in the meantime.
Thus, a second spacer screw is disclosed in the International Laid-Open Application 97/26460. A screw disclosed in this prior publication has a thread section which can be screwed into the base member, opposite this a head section having a plurality of circumferential ribs facing the rear end and a thread following on therefrom, and a shank region which in turn is arranged between the thread section which can be screwed into the base member and the thread of the head section. An essential feature of this screw is that the head section has a larger core diameter than the front thread section which can be screwed into the base member.
Furthermore, triangular notches are provided in the circumferential ribs and in the thread turns of the head section. Said notches form cutting edges which, on the one hand, facilitate the screwing of the associated thread into the structural member and, on the other hand, prevent the anchoring section from coming out of the structural member during correction of the spacing.
Although this screw has some advantages compared with the spacer screw described above, it is expensive to produce owing to its design with two different core diameters and is therefore scarcely suitable for efficient use on the building site.
Finally, a third spacer screw is disclosed in European Laid-Open Application 0 801 233. The countersunk screw disclosed therein is formed essentially in the same way as the screw disclosed in WO/97/26460, i.e. has a thread section which can be screwed into the base member, a head section with at least two circumferential ribs and a thread following on therefrom, and a shank region arranged in between.
The essential feature of this third spacer screw is that the thread of the head section has a larger external diameter than the thread section in the point region.
It is known that both the screw of WO/97/26460 and that of EP-A 0 801 233 cannot always be driven easily, i.e. with as little force as possible, into the structural member to be fastened. In addition, these two spacer screws also have the further disadvantage that, when they are used, a desired distance between base member and structural member can be established only when the thread of the head section is screwed virtually completely out of the structural member, and that therefore, in the case of structural members with relatively large wall thicknesses, the screw head must be screwed far into the structural member, which has an adverse effect on the stability properties of the fastened members.